WET theme: Replace PNG with gradient

- Use filter gradient for old IE and hide vendor prefixes for *-ie.css
- Fix gradient call to emit vendor prefixed linear gradients
WET theme: Remove unreferenced search images

Apparently not used in this theme
Base theme: Replace gradient images with CSS

- Banner.png wasn't referenced
- Add gradient versions of search button images in modern and oldIE
browsers
Merge pull request #1682 from pjackson28/master

Fixed SVG images not displaying in IE10 #1679.
Merge pull request #1683 from pjackson28/master

Smoothed out loading of SVG images in IE10
Merge pull request #1680 from nschonni/wet-theme-css-gradient

Replace WET theme css gradient images
Merge pull request #1681 from nschonni/base-theme-replace-gradient-images

Base theme: Replace gradient images with CSS
Fixed broken links.
Merge pull request #1684 from EricDunsworth/v3.1-broken-link-fixes

Geomap: Fixed broken links.
Sign in/out CSS code
HTML working examples for sign in/out
Added overlay timeout to Geomap to allow plugins to continue loading when one or more data sources fail.
Merge pull request #1687 from pjackson28/geomap-fix

Added overlay timeout to Geomap to allow plugins to continue loading when one or more data sources fail
Merge pull request #1685 from patheard/wb-session

Sign In/Out CSS/HTML for #338
Added i18n strings for terms for sign in/sign out.
Extended Sign In/Sign Out to mobile view. Added Spanish examples. Added GC Web Usability Intranet theme examples.
Added Sign In/Sign Out examples to the WET and Base themes.
Merge pull request #1688 from pjackson28/signinout-mobile

Extended Sign In/Sign Out to mobile view as well as to the GCWU Intranet, WET and Base themes
Added space after :
Merge pull request #1689 from patheard/wb-session-scss

Fixed CSS of #wb-session to match style guide